Method for making bobbins



Aug- 30, 1950 A. FoLTA METHOD FOR MAKING BOBBINS Filed Dec. 11, 1956 ATTORNEY /NVENTORJ 5y @Maw l in.. A

United States Patent C) METHQD FOR MAKING BBBINS Andrew Folia, Lakewood, Ohio, assigner to Precision Paper Tube Company, Chicago, Ill., a corporation of Illinois Filed Dec. 11, 1956, Ser. No. 627,644

'5 Claims. (Cl. 29-458) This invention relates to a method for making bobbins, and more specifically, to an improvement in the method for making bobbins or electrical coil forms disclosed in U.S. Patent No. 2,736,956, issued March 6, l956.

The above-cited patent sets forth a relatively fast and economical method for producing the coil forms cornmonly used in the electrical industry for holding transformer windings and the like. Formerly, the bobbins were assembled by placing the terminal flanges upon the ends of the cores and then swaging the core ends to lock the flanges in place. Since each bobbin required individual swag-ing, it is evident that this conventional mode of manufacture necessitated expensive machinery and consumed considerable time.

Patent No. 2,736,956 discloses a method for mass producing such bobbins without swaging the core ends to lock the flanges thereon. Instead, the laminated paper cores are coated with a thin layer of plastic capable of permanently expanding when reacted with a swelling agent or agents. The apertured fiber flanges are then slipped upon the ends of the core and the assembly is dipped into a bath composed of the selected swelling agents to swell the plastic coating and securely anchor the flanges upon the core between the swollen zones of increased thickness. The expanded plastic coating is then heated and dried to permanently lock the flanges in place. Thus, the flanges are anchored by abutments on both sides thereof that rise laterally or outwardly from the core. v In general, the treating bath should contain a swelling agent combined with solvents for softening the cores plastic coating. While the particular chemicals and their proportions may vary considerably, the patent teaches that a ketone such as methyl isobutyl ketone, is particularly effective as a swelling agent when the plastic coating upon the core consists of cellulose acetate. Such a swelling agent may be combined with a plurality of solvents having different time characteristics to produce a bath which will quickly and effectively soften and swell the cores plastic layer. For instance, an effective treating bath may be prepared by mixing the swelling agent with an extremely active solvent, such as tetrahydrofuran, a somewhat less active solvent, such as acetone, and a mild softening solvent, such as ethylene glycol monometbyl ether.

The bobbins manufactured by the above-described method are used principally as forms upon which electrical Wire is wound, the winding being wrapped about the cores between the end flanges anchored thereto. It is evident, therefore, that while the end flanges may be subjected to forces extending in Various directions, the principal concern is with those forces tending to urge the end flanges away from each other and off the ends of the core. The present invention deals with a particularly effective method for securely anchoring the flanges against such forces.

Therefore, a main object of the present invention is to provide an improved method for firmly locking the end eff- ICC anges upon a bobbin core, the method producing a coil form of increased structural rigidity in which the connections between the end flanges and the core are capable of withstanding forces of considerable magnitude directed outwardly along the longitudinal axis of that core and against the flanges. Other objects will appear from the specication and drawings, in which:

Fig. l is a perspective view of a bobbin or coil form embodying the present invention; Fig. 2 is a cross-sectional end View of the coil formas it appears prior to assembly, the core and terminal anges being shown separately; Fig. 3 is a sectional end view of an assembled coil form with the end flanges in an initial or first position; Fig. 4 is a sectional end view similar to Fig. 3, but showing the end flanges in a second or final position; and Fig. 5 is an enlarged broken sectional side View of a completely formed bobbin.

Referring to the drawings, Fig. l shows a bobbin or coil form 10 comprising a core 11 and end flanges 12. The core is shown as a conventional laminated paper core, and has a thin layer of plastic 13, preferably cellulose acetate, wound over the cores outer surface to form a continuous single layer thereon (Fig. 2). Such a coating or winding may be easily applied to the cores in the manufacturing process.

Like the core 11, the terminal flanges 12 may be conventional in all respects and are equipped with axial indentations 14 surrounding central apertures 15. The central aperture of each flange conforms in size and shape to the surface of the coated core 12 for snugly and slidably receiving that core.

It will be noted that the axial indentations 14 of the ilanges permit the construction of a coil form' in which small zones 16 of the core project outwardly beyond apertures 15 when the respective ends of the core are flush with the outer perpendicular surfaces of flanges 12. However, it is to be understood that planar terminal flanges without indentations 14 may be used where the particular application `does not require that the ends of the core lie along the same planes as the outer surfaces of the flanges.

In practicing the invention, core 11 is first coated or covered with its plastic layer 13 and flanges 12 are then placed over the core at the initial positions indicated in Fig. 3. Exact positioning of the flanges is unnecessary at this time; all that is required is that the flanges be disposed so that they may be slid along the coated core into the final position that they will occupy when the coil form is completed. While the flanges are in their initial positions, the coil form assembly is placed in a treating bath operative to soften and swell the plastic layer 13. The chemical composition of this bath has already been described above and is set forth in detail in Patent No. 2,7 36,956. Exposure to the softening and swelling agents of the bath for a 1-5 second period results in a substantial swelling of the plastic layer, as illustrated in Fig. 3.

After the assembly has been removed from the bath and while the swollen plastic layer is still in a soft or mastic state, flanges 12 are slid outwardly along the core 11 into their second or final positions (Fig. 4). Since the dimensions of the flange openings are smaller than the dimensions of the coated core when the plastic coating is in a swollen or enlarged state, movement of the flanges from their initial positions to their final locations results inthe displacement of a quantity of soft plastic material about the core. In other words, a squeegee action occurs and a portion of the plastic layer in the zone of flange-movement is pushed outwardly ahead of the apertured flanges. This squeegeed or displaced plastic material forms a bead or rim 17 about each end of the core and adjacent the outer surfaces of the respective flanges when those flanges reach their final positions.

Movement of the flanges from their initial to their final positions may be performed either mechanically or manual-ly, depending upon the magnitude of the manu. facturing operation. It has been found, however, that mechanical repositioning is particularly suitable because of the uniform spacing between the paired flanges when those flanges are in their final positions and because of the flush relation between the core ends and the outer perpendicular surfaces of the respective flanges.

Preferably, the flanges are repositioned shortly before the treated plastic layer has reached a stage of maximum or full expansion. Therefore, the continued eX- pansion of the plastic remaining upon the core along the zone of flange movement after each of the flanges has been repositioned locks the respective flanges against return movement towardsV their original or initial positions.

After the flanges have been repositioned upon the bobbin cores, the coil forms are set aside until the plastic layers harden and dry. lf desired, the forms may be exposed to controlled heat in an oven to speed the drying process.

We have found that the coil forms produced by the improved method of the present invention are extremely sturdy and that the accumulations of swollen plastic material about the projecting portions 16 at the respective ends of each bobbin core provide mechanical flange-core connections which are substantially stronger in resisting outward opposing movement of the flanges than the connections produced by previously known methods. same time, the residuum of swollen plastic material between the flanges of each bobbin securely anchors those flanges against movement by forces which might otherwise drive the flanges into their original positions.

While the present invention is preferably practiced using agents capableof both softening and swelling the plastic layer, it is apparent that an interlock between the core and flanges may also be obtained where only softening agents are employed, especially where the size Y of the flange opening is slightly smaller than the size of the core with the softened coating thereon. Hence, if

only a portion of the core is coated and the flange (or flanges) is initially positioned upon an uncoated portion, movement of that flange over the coated portion while the plasticV is ina softened state will have the effect of squeegeeing a portion of the softened plastic to form a locking bead against the flange when the flange Vis in its final position.

While in the foregoing I have disclosed the method of the present invention in considerable detail for purposes of illustration, it will be understood by those skilled in the art that many of these details may be varied without departing from the spirit and scope of the invention.

l. ln a method for making bobbins, the steps of coverl ing at least a portion of a core with a plastic material capable of softening and permanently swelling when dipped in a bath having agents selected to soften and permanently swell the same and of hardening after removal from said bath, and placing a -flange in an initial positionup-on said core remote from an end thereof, dipping said core and flange into a bath containing agents operative to soften and permanently swell said plastic covering, sliding said flange towards said end into a final positionk upon said core while said plastic is softened to squeegee a portion of the same into a zone at said end of said core adjacent said flange when the same is in its final position, and thereafter permitting said plastic to harden while said flange Vis in its final position.

2. ln a method for securing a flange in position upon the end of a core, the steps of coating said core with a layer of material adapted to soften and swell upon appropriate treatment thereof and to pass into a hardened.

At thestate following such treatment, placing said flange in an initial position upon said coated core remote from said end thereof, treating said layer to soften and permanently swell the same, sliding said flange towards said end to a final position upon said coated core while said layer is in a softened state to squeegee a portion of said layer along the zone of movement of said flange and to accumulate a quantity of said material at the end of the core adjacent said flange when the same is Yin its nal position, and thereafter permitting said plastic to pass into its hardened state while said flange is in its final position.

3. ln a method for securing a flange in position upon a core adjacent an end thereof, the steps of providing a flange and core, covering said core with a layer of material capable of softening and swelling upon treatment with an appropriate swelling agent and of passing into a hardened and permanently swollen state following such treatment, placing said flange in an initial position upon said core and layer remote from the end of the core, treating said layer with an agent capable of softening and permanently swelling the same, sliding said kflange towards the end of the core to a final position upon said core and layer while said layer Vis in a softened and swollen state to displace a portion of said `layer and to accumulate a quantity of said material adjacent the flange when the same is in its final position, and thereafter permitting said material to pass into its hardened state while said flange is in its final position.

4. in a method for making bobbins, the steps of providing a core and a flange, covering said core with a relatively thin layer of plastic capable of softening and swelling upon appropriate treatment thereof and of drying into a hardened and permanently swollen state `following such treatment, placing said flange in a first position upon said core and plastic covering, dipping said core and flange into a bath containing agents adapted to soften and permanently swell said plastic, displacing a surface portion of said plastic covering by shifting said flange along said core and into a final position while said swollen plastic is still in a softened state and before it is fully swollen, permitting said swelling of said plastic to continue after said flange is in its final position and confined against the displaced portion of saidplastic covering, and thereafter permitting Vsaid plastic to dry into its hardened and permanently` swollen state.

5. in a method for makingrbobbins, the steps of providing a core and coating the same vwith a relatively thin layerV of plastic having the property of softening'and permanently swelling when dipped in a bath having agents selected to soften and swell the same and of passing into a hardened state following removal from saidY bath, providing a flange having an opening therethrough adapted to snugly -flt over said core and layer of plastic, placing said flange in a first position upon said core ,and plastic layer, dipping said core and flange into a bath containing agents operative to soften and permanently swell said layer of plastic, sliding said flange into a final position upon said lcore while said plastic is softened and swelling to squeegee a portion of the same into a zone adjacent said flange when thesame is in its nalposition, said sliding step being performed beforesaid softened plastic is Vcompletely swollen, permitting said swelling to continue after said flange is atV its final position'and confined against said squeegeed portion, and thereafter permitting said plastic to pass into its hardened state to lock said flange upon said core.

References Cited in the file of this patent UNITED STATES PATENTS 

